Pneumatic tire

ABSTRACT

Provided is a pneumatic tire for which rolling resistance at high speed running is sufficiently reduced and durability is sufficiently improved. The pneumatic tire has a side portion, a thickness S (mm) of a rubber layer radially outside a carcass on the side portion at the maximum tire width position is 3 mm or less, the loss tangent of the rubber layer measured under the conditions of 70° C., a frequency of 10 Hz, an initial distortion of 5%, and a dynamic distortion rate of 1% is 0.15 or less, and when the cross-sectional width of the tire is Wt (mm) and the outer diameter is Dt (mm) when installed on a regular rim and the internal pressure is 250 kPa, the volume of the space occupied by the tire is the virtual volume V (mm3), the following (formula 1) and (formula 2) are satisfied.1700≤(Dt2×π/4)/Wt≤2827.4  (formula 1)[(V+1.5×107)/Wt]≤2.88×105  (formula 2)

TECHNICAL FIELD

The present disclosure relates to a pneumatic tire.

BACKGROUND ART

In recent years, from the viewpoint of increasing interest in environmental issues and economic efficiency, there has been a growing demand for fuel efficiency in automobiles, and there is a strong demand for improved fuel efficiency also in pneumatic tires (hereinafter, simply referred to as “tires”) installed in automobiles.

The fuel efficiency of a tire can be evaluated by rolling resistance, and it is known that the smaller the rolling resistance, the better the fuel efficiency of the tire.

Therefore, conventionally, it has been proposed to reduce the rolling resistance by devising the formulation of the rubber composition constituting the tread portion of the tire (for example, Patent Documents 1 to 4).

PRIOR ART DOCUMENTS Patent Document

-   [Patent Document 1] JP2018-178034A -   [Patent Document 2] JP2019-089911A -   [Patent Document 3] WO2018/186367A -   [Patent Document 4] JP2019-206643A

SUMMARY OF INVENTION Problem to be Solved by the Invention

However, it cannot be said that the tire manufactured by the above-mentioned conventional technology is sufficiently reduced in rolling resistance during high-speed running, and further reduction is desired. And it cannot be said that these tires have sufficient durability.

Therefore, an object of the present disclosure is to provide a pneumatic tire in which the rolling resistance during high-speed running is sufficiently reduced and its durability is sufficiently improved.

Means for Solving the Problem

The present discloser has diligently studied the solution to the above-mentioned problem, found that the above-mentioned problem can be solved by the disclosure described below, and has completed the present disclosure.

The present disclosure is;

-   -   a pneumatic tire having a side portion, wherein     -   the thickness S (mm) of the rubber layer radially outside the         carcass of the side portion at the maximum width position of the         tire is 3 mm or less;     -   the loss tangent (70° C. tan δ) of the rubber layer is 0.15 or         less measured under the conditions of 70° C., frequency of 10         Hz, initial strain of 5%, and dynamic strain rate of 1%; and     -   when the cross-sectional width of the tire is Wt (mm), the outer         diameter is Dt (mm), and the volume of the space occupied by the         tire is the virtual volume V (mm³), when the tire is installed         on a standardized rim and the internal pressure is 250 kPa, the         tire satisfies following (formula 1) and (formula 2):

1700≤(Dt ²×π/4)/Wt≤2827.4  (formula 1)

[(V+1.5×10⁷)/Wt]≤2.88×10⁵  (formula 2)

The Effect of the Invention

According to the present disclosure, it is possible to provide a pneumatic tire in which the rolling resistance during high-speed running is sufficiently reduced and its durability is sufficiently improved.

EMBODIMENTS FOR CARRYING OUT THE INVENTION [1] Features of the Tire of the Present Disclosure

First, the features of the tire according to the present disclosure will be described.

1. Overview

The tire according to the present disclosure is characterized in that the thickness S (mm) of the rubber layer radially outside the carcass of the side portion at the maximum width position of the tire is 3 mm or less, and the loss tangent (70° C. tan δ) of the rubber composition is 0.15 or less measured under the conditions of 70° C., frequency of 10 Hz, initial strain of 5%, and dynamic strain rate of 1%.

The tire according to the present disclosure is characterized also in that, when the cross-sectional width of the tire is Wt (mm), the outer diameter is Dt (mm), and the volume of the space occupied by the tire is the virtual volume V (mm³), when the tire is installed on a standardized rim and the internal pressure is 250 kPa, the tire satisfies following (formula 1) and (formula 2):

1700≤(Dt ²×π/4)/Wt≤2827.4  (formula 1)

[(V+1.5×10⁷)/Wt]≤2.88×10⁵  (formula 2)

The rubber layer forming the side portion and the shape of the tire have the characteristics described above, and thereby a tire with sufficiently reduced rolling resistance during high-speed running and sufficiently improved durability can be provided.

In the above description, the “standardized rim” is a rim defined for each tire in the standard system including the standard on which the tire is based. For example, in the case of JATMA (Japan Automobile Tire Association), it is the standard rim in applicable sizes described in the “JATMA YEAR BOOK”, in the case of “ETRTO (The European Tire and Rim Technical Organization)”, it is “Measuring Rim” described in “STANDARDS MANUAL”, and in the case of TRA (The Tire and Rim Association, Inc.), it is “Design Rim” described in “YEAR BOOK”. In the case of tires that are not specified in the standard, it refers a rim that can be assembled and can maintain internal pressure, that is, the rim that does not cause air leakage from between the rim and the tire, and has the smallest rim diameter, and then the narrowest rim width.

Further, the outer diameter Dt of the tire is the outer diameter of the tire installed on a standardized rim, having an internal pressure of 250 kPa and in a no-load state. The cross-sectional width Wt (mm) of the tire is the width of tire installed on a standardized rim, having an internal pressure of 250 kPa and in a no-load state, and is the distance excluding patterns, letters, and the like on the tire side from the linear distance between the sidewalls (total width of the tire) including all the patterns, letters and the like on the tire side.

Further, the virtual volume V (mm³) of the tire is, specifically, can be calculated by the following formula:

V=[(Dt/2)²−{(Dt/2)−Ht} ² ]×π×Wt

based on the outer diameter of tire Dt (mm), the tire cross-sectional height (distance from the bottom of the bead to the outermost surface of the tread; ½ of the difference between the tire outer diameter and the nominal rim diameter) Ht (mm), and the cross-sectional width of tire Wt (mm), in the state the tire is installed on a standardized rim, the internal pressure is 250 kPa and no load is applied.

2. Mechanism of Effect Manifestation in Tire According to the Present Disclosure

The mechanism of effect manifestation in the tire according to the present disclosure, that is, the mechanism of the rolling resistance being sufficiently reduced at high-speed running, and the durability being sufficiently improved, is presumed as follows.

(1) Tire Shape

As described above, in the present disclosure, the cross-sectional width Wt (mm) and the outer diameter Dt (mm) of the tire are tried to satisfy 1700≤(Dt²×π/4)/Wt≤2827.4 (formula 1).

By increasing the area when the tire is viewed from the lateral direction, [(Dt/2)²×π)=(Dt²×π/4)], with respect to the cross-sectional width Wt of the tire, and satisfying the numerical range specified in (formula 1), the repetition of deformation per unit time is reduced, as a result, the time that can be used for heat exchange is increased, thereby improving the heat release property of the side portion, and the friction between the tread portion and the road surface can be reduced, and it is considered that the durability and low rolling resistance of the tire can be improved

In (formula 1), (Dt²×π/4)/Wt is more preferably 1735 or more, further preferably 1737 or more, further preferably 1749 or more, further preferably 1751 or more, further preferably 1753 or more, further preferably 1758 or more, further preferably 1760 or more, further preferably 1787 or more, further preferably 1801 or more, further preferably 1818 or more, further preferably 1853 or more, further preferably 1856 or more, further preferably 1864 or more, further preferably 1865 or more, further preferably 1963.4 or more, further preferably 2004 or more, further preferably 2018 or more, further preferably 2027 or more, further preferably 2030 or more, further preferably 2033 or more, and further preferably 2113 or more.

However, since the centrifugal force of such a tire increases during rolling, the radius of the tire grows greatly during rolling and the tread portion becomes thinner accordingly, damage may occur, when an impact is applied to the tread portion. In addition, since the outer diameter increases due to centrifugal force, the amount of deformation of the side portions also increases, so there is room for improvement in terms of rolling resistance during high-speed running.

Therefore, in the present disclosure, the virtual volume V (mm³) and the cross-sectional width Wt (mm) of the tire are tried to satisfy [(V+1.5×10⁷)/Wt]≤2.88×10⁵ (formula 2).

In this way, it is considered that, by reducing the virtual volume V of the tire in accordance with the decrease in the cross-sectional width Wt of the tire, and reducing the volume of the tire itself, the growth rate of the outer diameter due to the centrifugal force can be reduced, and the damage resistance of the tread portion can be improved when the impact is applied on the tread portion. In addition, it is considered that the amount of deformation of the side portion can be reduced by suppressing the growth of the outer diameter of the tire.

[(V+1.5×10⁷)/Wt] is more preferably 2.87×10⁵ or less, further preferably 2.86×10⁵ or less, further preferably 2.77×10⁵ or less, further preferably 2.60×10⁵ or less, further preferably 2.58×10⁵ or less, further preferably 2.54×10⁵ or less, further preferably 2.50×10⁵ or less, further preferably 2.42×10⁵ or less, further preferably 2.26×10⁵ or less, further preferably 2.25×10⁵ or less, further preferably 2.24×10⁵ or less, further preferably 2.21×10⁵ or less, further preferably 2.20×10⁵ or less, further preferably 2.19×10⁵ or less, and further preferably 2.16×10⁵ or less.

At this time, it is more preferable that [(V+2.0×10⁷)/Wt]≤2.88×10⁵ (Formula 3), and further preferable that [(V+2.5×10⁷)/Wt]≤2.88×10⁵ (Formula 4).

The above [(V+2.0×10⁷)/Wt] is further preferably 2.83×10⁵ or less, further preferably 2.79×10⁵ or less, further preferably 2.77×10⁵ or less, further preferably 2.64×10⁵ or less, further preferably 2.49×10⁵ or less, further preferably 2.47×10⁵ or less, further preferably 2.46×10⁵ or less, further preferably 2.45×10⁵ or less, and further preferably 2.44×10⁵ or less.

Further, [(V+2.5×10⁷)/Wt] is further preferably 2.86×10⁵ or less, further preferably 2.77×10⁵ or less, further preferably 2.76×10⁵ or less, further preferably 2.72×10⁵ or less, further preferably 2.71×10⁵ or less, further preferably 2.70×10⁵ or less, further preferably 2.69×10⁵ or less, and further preferably 2.68×10⁵ or less.

(2) Rubber Composition Forming a Tread Portion

In the present disclosure, the rubber layer forming the side portion has a thickness S (mm) radially outside the carcass of the side portion at the tire maximum width position being 3 mm or less, and a loss tangent (70° C. tan δ) measured under the conditions of 70° C., frequency of 10 Hz, initial strain of 5% and dynamic strain rate of 1% being 0.15 or less.

As a result, heat generation in the side portion can be reduced and the heat release property of the side portion can be further improved, so the outer diameter of the tire can be suppressed from increasing due to the expansion of the air inside the tire, and it is considered that the durability and he low rolling resistance during high-speed running can be further improved. The 70° C. tan α is more preferably 0.11 or less, and even more preferably 0.07 or less.

Measurement of the above-mentioned 70° C. tan α is performed on the rubber cut out from the radially outside of the groove bottom of the tire at least, preferably from the radially outside of the half depth of the deepest circumferential groove. Specifically, the measurement is performed using, for example, a viscoelasticity measuring device of “Eplexor (registered trademark)” manufactured by GABO. When the rubber layer forming the side portion is formed of a plurality of layers, the 70° C. tan α of one of the layers should be 0.15 or less.

[2] More Preferable Embodiment of the Tire According to the Present Disclosure.

The tire according to the present disclosure can obtain a larger effect by taking the following embodiment.

1. Aspect Ratio

The tire according to the present disclosure is preferably a tire having an aspect ratio of 40% or more, whereby, since the area of the side portion can be increased, the heat release property can be further improved, the rolling resistance during high-speed running can be further reduced, and the durability of the tire can be further improved.

The aspect ratio (%) described above can be obtained by the following formula using the cross-sectional height Ht (mm) and the cross-sectional width Wt (mm) of the tire when the internal pressure is 250 kPa.

(Ht/Wt)×100(%)

The aspect ratio is more preferably 45% or more, further preferably 47.5% or more, further preferably 49% or more, further preferably 50% or more, further preferably 51% or more, further preferably 52.5% or more, further preferably 53% or more, further preferably 55% or more, and further preferably 58% or more. There is no particular upper limit, but for example, it is 100% or less.

2. Side Rubber Layer

When the side portion is thick and has a large area, the amount of generated heat may be greater than the amount of heat release from the side portion. Therefore, the relationship between (V/Wt)×S, which is an index related to the volume of the side portion, and 70° C. tan δ, which is an index related to heat generation, was examined. As a result, it has been found that if 70° C. tan δ×(V/Wt)×S≤80000 (formula 5) is satisfied, the generation of heat can be appropriately controlled, rolling resistance during high-speed running can be further reduced, and durability of the tire can be further enhanced.

It is more preferable if 70° C. tan α×(V/Wt)×S≤60000 (formula 6). It is further preferable if 70° C. tan α×(V/Wt)×S≤40000 (formula 7) and 70° C. tan δ×(V/Wt)×S≤35000 (formula 8).

More specifically, the 70° C. tan δ×(V/Wt)×S is more preferably 72,750 or less, further preferably 69,624 or less, further preferably 63,398 or less, further preferably 59,631 or less, further preferably 58129 or less, further preferably 54900 or less, further preferably 52171 or less, further preferably 47994 or less, further preferably 44385 or less, further preferably 33673 or less, further preferably 31884 or less, more preferably 30104 or less, more preferably 29515 or less, further preferably 27847 or less, further preferably 27519 or less, further preferably 16626 or less, further preferably 15078 or less, and further preferably 13725 or less.

3. Tire Shape

In the tire according to the present disclosure, when the tire is installed on a standardized rim and the internal pressure is 250 kPa, the specific outer diameter Dt (mm) is preferably, for example, 515 mm or more, more preferably 558 mm or more, further preferably 585 mm or more, further preferably 649 mm or more, further preferably 658 mm or more, further preferably 663 mm or more, further preferably 664 mm or more, further preferably 665 mm or more, further preferably 672 mm or more, and most preferably 673 mm or more.

On the other hand, it is preferably less than 843 mm, more preferably 734 mm or less, further preferably less than 725 mm, further preferably 718 mm or less, further preferably 717 mm or less, further preferably 716 mm or less, further preferably 713 mm or less, further preferably 710 mm or less, further preferably less than 707 mm, further preferably 692 mm or less, further preferably 691 mm or less, further preferably less than 685 mm, further preferably 684 mm or less, further preferably 680 mm or less, further preferably 679 mm or less, and further preferably 674 mm or less.

The specific cross-sectional width Wt (mm) is, for example, preferably 115 mm or more, more preferably 130 mm or more, further preferably 150 mm or more, further preferably 170 mm or more, still more preferably 175 mm or more, still more preferably 176 mm or more, still more preferably 177 mm or more, still more preferably 178 mm or more, still more preferably 181 mm or more, still more preferably 182 mm or more, even more preferably 185 mm, and most preferably 193 mm or more.

On the other hand, it is preferably less than 305 mm, more preferably less than 245 mm, further preferably 231 mm or less, further preferably 229 mm or less, further preferably 228 mm or less, further preferably 227 mm or less, further preferably 226 mm or less, further preferably 225 mm or less, further preferably less than 210 mm, further preferably less than 205 mm, further preferably 202 mm or less, further preferably 201 mm or less, further preferably 200 mm or less, further preferably less than 200 mm, further preferably 199 mm or less, further preferably 198 mm or less, and further preferably 196 mm or less.

The specific cross-sectional height Ht (mm) is, for example, preferably 37 mm or more, more preferably 69 mm or more, further preferably 70 mm or more, further preferably 71 mm or more, further preferably 78 mm or more, further preferably 79 mm or more, further preferably 80 mm or more, further preferably 87 mm or more, further preferably 89 mm or more, further preferably 90 mm or more, further preferably 95 mm or more, further preferably 96 mm or more, further preferably 98 mm or more, and further preferably 99 mm or more.

On the other hand, it is preferably less than 180 mm, more preferably 117 mm or less, further preferably 113 mm or less, further preferably less than 112 mm, further preferably 104 mm or less, and further preferably 101 mm or less.

The specific virtual volume V is preferably 13,000,000 mm³ or more, more preferably 23,136,067 mm³ or more, further preferably 23,206,160 mm³ or more, further preferably 23,672,177 mm³ or more, further preferably 28,431,992 mm³ or more, further preferably 28,526,824 mm³ or more, further preferably 29,000,000 mm³ or more, further preferably 29,087,378 mm³ or more, further preferably 30,111,710 mm³ or more, further preferably 30,354,118 mm³ or more, further preferably 34,196,412 mm³ or more, further preferably 35,417,448 mm³ or more, further preferably 35,785,417 mm³ or more, further preferably 35,954,077 mm³ or more, further preferably 36,000,000 mm 3 or more, further preferably 36,203,610 mm³ or more, and further preferably 37,040,131 mm³ or more.

On the other hand, it is preferably less than 66,000,000 mm³, more preferably 50,043,281 mm³ or less, further preferably less than 44,000,000 mm³, further preferably 43,478,150 mm³ or less, further preferably 42,618,582 mm³ or less, further preferably 40,161,995 mm³ or less, and further preferably less than 38,800,000 mm³.

Further, in the present disclosure, considering the stability of the riding comfort during running, (Dt−2×Ht) is preferably 450 mm or more, more preferably 457 mm or more, further preferably 470 mm or more, further preferably 480 mm or more, further preferably 482 mm or more, and further preferably 484 mm or more.

On the other hand, considering the deformation of the tread portion, it is preferably less than 560 mm, more preferably 559 mm or less, further preferably 558 mm or less, further preferably 534 mm or less, further preferably 533 mm or less, further preferably 532 mm or less, further preferably less than 530 mm, further preferably less than 510 mm, further preferably 508 mm or less, further preferably 507 mm or less, and further preferably 506 mm or less.

[3] Embodiment

Hereinafter, the present disclosure will be specifically described based on the embodiments.

1. Rubber Composition Forming the Side Portion

The rubber composition forming the side portion of the tire according to the present disclosure can be obtained by appropriately adjusting the type and amount of various compounding materials such as rubber components, fillers, softeners, vulcanizing agents and vulcanization accelerators described below.

(1) Rubber Component

In the present embodiment, as the rubber component, rubber (polymer) generally used for producing tires such as butadiene rubber (BR), styrene-butadiene rubber (SBR), isoprene-based rubber, and nitrile rubber (NBR) can be used. Among these, it is preferable to use butadiene rubber (BR) and isoprene-based rubber.

(a) BR

The content of BR in 100 parts by mass of the rubber component is, for example, preferably 40 parts by mass or more, more preferably 50 parts by mass or more, and even more preferably 55 parts by mass or more from the viewpoint of wear resistance. On the other hand, from the viewpoint of maintaining rolling resistance during high-speed running, the content is preferably 75 parts by mass or less, more preferably 70 parts by mass or less, and even more preferably 65 parts by mass or less.

The weight average molecular weight of BR is, for example, more than 100,000 and less than 2 million. The vinyl bond amount of BR is, for example, more than 1% by mass and less than 30% by mass. The cis content of BR is, for example, more than 1% by mass and less than 98% by mass. The trans amount of BR is, for example, more than 1% by mass and less than 60% by mass. The cis content can be measured by infrared absorption spectrometry.

BR is not particularly limited, and BR with high cis content (90% or more of cis content), BR with low cis content, BR containing syndiotactic polybutadiene crystals, and the like can be used. BR may be either non-modified BR or modified BR. As modified BR, for example, BR modified with a compound (modifying agent) represented by the following formula can be used.

In the formula, R¹, R² and R³ represent, the same or different, alkyl group, alkoxy group, silyloxy group, acetal group, carboxyl group (—COOH), mercapto group (—SH) or derivatives thereof. R⁴ and R⁵ represent, the same or different, hydrogen atoms or alkyl groups. R⁴ and R⁵ may be combined to form a ring structure with nitrogen atoms. n represents an integer.

As the modified BR modified with the compound (modifier) represented by the above formula, a BR whose polymer terminal (active terminal) has been modified with the compound represented by the above formula can be used.

As R¹, R² and R³, an alkoxy group is preferable (preferably an alkoxy group having 1 to 8 carbon atoms, more preferably an alkoxy group having 1 to 4 carbon atoms). As R⁴ and R⁵, an alkyl group (preferably an alkyl group having 1 to 3 carbon atoms) is preferable. n is preferably 1 to 5, more preferably 2 to 4, and even more preferably 3. Further, when R⁴ and R⁵ are bonded to form a ring structure together with a nitrogen atom, a 4- to 8-membered ring is preferable. The alkoxy group also includes a cycloalkoxy group (for example, cyclohexyloxy group) and an aryloxy group (for example, phenoxy group, benzyloxy group).

Specific examples of the above modifying agent include 2-dimethylaminoethyltrimethoxysilane, 3-dimethylaminopropyltrimethoxysilane, 2-dimethylaminoethyltriethoxysilane, 3-dimethylaminopropyltriethoxysilane, 2-diethylaminoethyltrimethoxysilane, 3-diethylaminopropyltrimethoxysilane, 2-diethylaminoethyltriethoxysilane, and 3-diethylaminopropyltriethoxysilane. These may be used alone or in combination of two or more.

Further, as the modified BR, a modified BR modified with the following compound (modifying agent) can also be used. Examples of the modifying agent include polyglycidyl ethers of polyhydric alcohols such as ethylene glycol diglycidyl ether, glycerin triglycidyl ether, trimethylolethanetriglycidyl ether, and trimethylolpropane triglycidyl ether;

-   -   polyglycidyl ethers of aromatic compounds having two or more         phenol groups such as diglycidylated bisphenol A;     -   polyepoxy compounds such as 1,4-diglycidylbenzene,         1,3,5-triglycidylbenzene, and polyepoxidized liquid         polybutadiene;     -   epoxy group-containing tertiary amines such as         4,4′-diglycidyl-diphenylmethylamine, and         4,4′-diglycidyl-dibenzylmethylamine;     -   diglycidylamino compounds such as diglycidylaniline, N,         N′-diglycidyl-4-glycidyloxyaniline, diglycidyl orthotoluidine,         tetraglycidylmetaxylenidiamine,         tetraglycidylaminodiphenylmethane,         tetraglycidyl-p-phenylenediamine,         diglycidylaminomethylcyclohexane, and         tetraglycidyl-1,3-bisaminomethylcyclohexane;     -   amino group-containing acid chlorides such as         bis-(1-methylpropyl) carbamate chloride, 4-morpholincarbonyl         chloride, 1-pyrrolidincarbonyl chloride, N, N-dimethylcarbamide         acid chloride, and N, N-diethylcarbamide acid chloride;     -   epoxy group-containing silane compounds such as         1,3-bis-(glycidyloxypropyl)-tetramethyldisiloxane, and         (3-glycidyloxypropyl)-pentamethyldisiloxane;     -   sulfide group-containing silane compound such as         (trimethylsilyl) [3-(trimethoxysilyl) propyl] sulfide,         (trimethylsilyl) [3-(triethoxysilyl) propyl]sulfide,         (trimethylsilyl) [3-(tripropoxysilyl) propyl] sulfide,         (trimethylsilyl) [3-(tributoxysilyl) propyl] sulfide,         (trimethylsilyl) [3-(methyldimethoxysilyl) propyl] sulfide,         (trimethylsilyl) [3-(methyldiethoxysilyl) propyl] sulfide,         (trimethylsilyl) [3-(methyldipropoxysilyl) propyl] sulfide, and         (trimethylsilyl) [3-(methyldibutoxysilyl) propyl] sulfide;     -   N-substituted aziridine compound such as ethyleneimine and         propyleneimine;     -   alkoxysilanes such as methyltriethoxysilane, N, N-bis         (trimethylsilyl)-3-aminopropyltrimethoxysilane, N, N-bis         (trimethylsilyl)-3-aminopropyltriethoxysilane, N, N-bis         (trimethylsilyl) aminoethyltrimethoxysilane, and N, N-bis         (trimethylsilyl) aminoethyltriethoxysilane;     -   (thio) benzophenone compound having an amino group and/or a         substituted amino group such as 4-N,         N-dimethylaminobenzophenone, 4-N, N-di-t-butylaminobenzophenone,         4-N, N-diphenylamino benzophenone, 4,4′-bis (dimethylamino)         benzophenone, 4,4′-bis (diethylamino) benzophenone, 4,4′-bis         (diphenylamino) benzophenone, and N, N, N′,         N′-bis-(tetraethylamino) benzophenone;     -   benzaldehyde compounds having an amino group and/or a         substituted amino group such as 4-N,         N-dimethylaminobenzaldehyde, 4-N, N-diphenylaminobenzaldehyde,         and 4-N, N-divinylamino benzaldehyde;     -   N-substituted pyroridone such as N-methyl-2-pyrrolidone,         N-vinyl-2-pyrrolidone, N-phenyl-2-pyrrolidone,         N-t-butyl-2-pyrrolidone, and N-methyl-5-methyl-2-pyrrolidone;     -   N-substituted piperidone such as methyl-2-piperidone,         N-vinyl-2-piperidone, and N-phenyl-2-piperidone;     -   N-substituted lactams such as N-methyl-ε-caprolactam,         N-phenyl-ε-caprolactum, N-methyl-ω-laurilolactum,         N-vinyl-ω-laurilolactum, N-methyl-β-propiolactam, and         N-phenyl-β-propiolactam; and     -   N, N-bis-(2,3-epoxypropoxy)-aniline, 4,4-methylene-bis-(N,         N-glycidylaniline),         tris-(2,3-epoxypropyl)-1,3,5-triazine-2,4,6-triones, N,         N-diethylacetamide, N-methylmaleimide, N, N-diethylurea,         1,3-dimethylethylene urea, 1,3-divinylethyleneurea,         1,3-diethyl-2-imidazolidinone,         1-methyl-3-ethyl-2-imidazolidinone, 4-N,         N-dimethylaminoacetophenone, 4-N, N-diethylaminoacetophenone,         1,3-bis (diphenylamino)-2-propanone, and         1,7-bis(methylethylamino)-4-heptanone. The modification with the         above compound (modifying agent) can be carried out by a known         method. These modified BRs may be used alone or in combination         of two or more.

As BR, for example, products of Ube Industries, Ltd., JSR Corporation, Asahi Kasei Co., Ltd., Nippon Zeon Co., Ltd., etc. can be used.

(b) Isoprene Rubber

The content (total content) of the isoprene-based rubber in 100 parts by mass of the rubber component is preferably 25 parts by mass or more, more preferably 30 parts by mass or more, and further preferably 35 parts by mass or more, from the viewpoint of obtaining good low heat generation and durability during high-speed running. On the other hand, it is preferably 55 parts by mass or less, more preferably 50 parts by mass or less, and further preferably 45 parts by mass or less.

Examples of the isoprene-based rubber include natural rubber (NR), isoprene rubber (IR), reformed NR, modified NR, and modified IR. Among them, NR is preferable from the viewpoint of excellent strength.

As the NR, for example, SIR20, RSS #3, TSR20 and the like, which are common in the tire industry, can be used. The IR is not particularly limited, and for example, IR 2200 and the like, which are common in the tire industry, can be used. Reformed NR includes deproteinized natural rubber (DPNR), high-purity natural rubber (UPNR), and the like. Modified NR includes epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), grafted natural rubber, and the like. Modified IR includes epoxidized isoprene rubber, hydrogenated isoprene rubber, grafted isoprene rubber, and the like. These may be used alone or in combination of two or more.

(c) SBR

The rubber component may contain SBR as required. At this time, the content of SBR in 100 parts by mass of the rubber component is, for example, 1 part by mass or more and less than 100 parts by mass. It is more preferably more than 5 parts by mass, and further preferably more than 15 parts by mass, and more than 25 parts by mass is particularly preferable. On the other hand, it is preferably less than 65 parts by mass, more preferably less than 55 parts by mass, and further preferably less than 45 parts by mass, and less than 35 parts by mass is particularly preferable.

The weight average molecular weight of SBR is, for example, more than 100,000 and less than 2 million. The styrene content of SBR is, for example, preferably more than 5% by mass and less than 50% by mass, more preferably more than 10% by mass and less than 40% by mass, and further preferably more than 20% by mass and less than 35% by mass. The vinyl bond amount (1,2-bonded butadiene unit amount) of SBR is, for example, more than 5% by mass and less than 70% by mass. The structure identification of SBR (measurement of styrene content and vinyl bond amount) can be performed using, for example, an apparatus of the JNM-ECA series manufactured by JEOL Ltd.

The SBR is not particularly limited, and for example, emulsion-polymerized styrene-butadiene rubber (E-SBR), solution-polymerized styrene-butadiene rubber (S-SBR) and the like can be used. The SBR may be either a non-modified SBR or a modified SBR, and these may be used alone or in combination of two or more.

The modified SBR may be any SBR having a functional group that interacts with a filler such as silica. Examples thereof include

-   -   end-modified SBR (end-modified SBR having the above functional         group at the terminal) in which at least one end of the SBR is         modified with a compound having the above functional group         (modifying agent),     -   main chain modified SBR having the functional group in the main         chain,     -   main chain terminal modified SBR having the functional group at         the main chain and the terminal (for example, a main chain         terminal modified SBR having the above functional group to the         main chain and having at least one end modified with the above         modifying agent), and     -   end-modified SBR which is modified (coupled) with a         polyfunctional compound having two or more epoxy groups in the         molecule, and into which an epoxy group or hydroxyl group has         been introduced,     -   As the SBR, for example, SBR manufactured and sold by Sumitomo         Chemical Co., Ltd., JSR Corporation, Asahi Kasei Co., Ltd.,         Nippon Zeon Co., Ltd., etc. can be used. The SBR may be used         alone or in combination of two or more.

(d) Other Rubber Components

Further, as another rubber component, the rubber composition may contain a rubber (polymer) generally used in the production of tires, such as nitrile rubber (NBR).

(2) Compounding Materials Other than Rubber Components

(a) Filler

In the present embodiment, the rubber composition preferably contains a filler. Specific examples of the filler include silica, carbon black, graphite, calcium carbonate, talc, alumina, clay, aluminum hydroxide, and mica. Among these, carbon black can be preferably used as the reinforcing agent. It is also preferable to use silica as a reinforcing agent, if necessary. In this case, it is preferable to use it in combination with a silane coupling agent.

(a-1) Carbon Black

The content of carbon black is, for example, preferably 10 parts by mass or more and 100 parts by mass or less, more preferably 30 parts by mass or more and 70 parts by mass or less, and further preferably 40 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the rubber component. As a result, it is possible to improve the crack growth resistance, durability, ultraviolet deterioration resistance, and the like of the tire.

Nitrogen adsorption specific surface area (N₂SA) of carbon black is, for example, more than 30 m²/g and less than 250 m²/g. The amount of dibutyl phthalate (DBP) absorbed by carbon black is, for example, more than 50 ml/100 g and less than 250 ml/100 g. The nitrogen adsorption specific surface area of carbon black is measured according to ASTM D4820-93, and the amount of DBP absorbed is measured according to ASTM D2414-93.

The carbon black is not particularly limited, and examples thereof includes furnace black (furnace carbon black) such as SAF, ISAF, HAF, MAF, FEF, SRF, GPF, APF, FF, CF, SCF and ECF; acetylene black (acetylene carbon black); thermal black (thermal carbon black) such as FT and MT; and channel black (channel carbon black) such as EPC, MPC and CC.

Commercially available products include, for example, products of Asahi Carbon Co., Ltd., Cabot Japan Co., Ltd., Tokai Carbon Co., Ltd., Mitsubishi Chemical Corporation, Lion Corporation, Shin Nikka Carbon Co., Ltd., Columbia Carbon Co., Ltd., etc. These may be used alone or in combination of two or more.

(a-2) Silica

The rubber composition preferably contains silica, if necessary. The BET specific surface area of the silica is preferably more than 140 m²/g, more preferably more than 160 m²/g, from the viewpoint of obtaining good durability performance. On the other hand, from the viewpoint of obtaining good rolling resistance at high-speed running, it is preferably less than 250 m²/g, and more preferably less than 220 m²/g. Moreover, the content of the silica with respect to 100 parts by mass of the rubber component is preferably more than 35 parts by mass, more preferably more than 40 parts by mass, and further preferably more than 45 parts by mass, from the viewpoint of obtaining good durability performance. On the other hand, from the viewpoint of obtaining good rolling resistance during high-speed running, it is preferably less than 70 parts by mass, more preferably less than 65 parts by mass, and further preferably less than 60 parts by mass. The above-mentioned BET specific surface area is the value of N₂SA measured by the BET method according to ASTM D3037-93.

Examples of silica include dry silica (anhydrous silica) and wet silica (hydrous silica). Among them, wet silica is preferable because it has large number of silanol groups.

As the silica, for example, products of Degussa, Rhodia, Tosoh Silica Co., Ltd., Solvay Japan Co., Ltd., Tokuyama Corporation, etc. can be used.

(a-3) Silane Coupling Agent

As mentioned above, the rubber composition preferably contains a silane coupling agent together with silica. The silane coupling agent is not particularly limited. Examples of the silane coupling agent include

-   -   sulfide-based ones such as         bis(3-triethoxysilylpropyl)tetrasulfide, bis         (2-triethoxysilylethyl)tetrasulfide, bis         (4-triethoxysilylbutyl)tetrasulfide,         bis(3-trimethoxysilylpropyl) tetrasulfide,         bis(2-trimethoxysilylethyl) tetrasulfide,         bis(2-triethoxysilylethyl)trisulfide,         bis(4-trimethoxysilylbutyl) trisulfide,         bis(3-triethoxysilylpropyl)disulfide, bis(2-triethoxysilylethyl)         disulfide, bis(4-triethoxysilylbutyl)disulfide,         bis(3-trimethoxysilylpropyl) disulfide,         bis(2-trimethoxysilylethyl)disulfide,         bis(4-trimethoxysilylbutyl)disulfide, 3-trimethoxysilylpropyl-N,         N-dimethylthiocarbamoyltetrasulfide, 2-triethoxysilylethyl-N,         N-dimethylthiocarbamoyltetrasulfide, and         3-triethoxysilylpropylmethacrylatemonosulfide;     -   mercapto-based ones such as 3-mercaptopropyltrimethoxysilane,         2-mercaptoethyltriethoxysilane, and NXT and NXT-Z manufactured         by Momentive;     -   vinyl-based ones such as vinyl triethoxysilane, and vinyl         trimethoxysilane;     -   amino-based ones such as 3-aminopropyltriethoxysilane and         3-aminopropyltrimethoxysilane;     -   glycidoxy-based ones such as γ-glycidoxypropyltriethoxysilane         and γ-glycidoxypropyltrimethoxysilane;     -   nitro-based ones such as 3-nitropropyltrimethoxysilane, and         3-nitropropyltriethoxysilane; and     -   chloro-based ones such as 3-chloropropyltrimethoxysilane and         3-chloropropyltriethoxysilane. These may be used alone or in         combination of two or more.

As the silane coupling agent, for example, products of Degussa, Momentive, Shinetsu Silicone Co., Ltd., Tokyo Chemical Industry Co., Ltd., Azumax Co., Ltd., Toray Dow Corning Co., Ltd., etc. can be used.

The content of the silane coupling agent is, for example, more than 3 parts by mass and less than 15 parts by mass with respect to 100 parts by mass of silica.

(a-4) Other Fillers

The rubber composition may further contain fillers such as graphite, calcium carbonate, talc, alumina, clay, aluminum hydroxide, and mica, which are generally used in the tire industry, in addition to the above-mentioned carbon black and silica. These contents are, for example, more than 0.1 part by mass and less than 200 parts by mass with respect to 100 parts by mass of the rubber component.

(b) Softener

The rubber composition may contain oil (including extender oil), liquid rubber, or the like, as a softener. The total content of these is preferably more than 5 parts by mass, more preferably more than 10 parts by mass, and further more than 12 parts by mass with respect to 100 parts by mass of the rubber component. On the other hand, less than 30 parts by mass is preferable, less than 20 parts by mass is more preferable, and less than 17 parts by mass is further preferable. The oil content also includes the amount of oil contained in rubber (oil-extended rubber).

Examples of the oil include mineral oil, generally referred to as process oil, vegetable oil and fat, and a mixture thereof. As the mineral oil (process oil), for example, a paraffinic process oil, an aroma-based process oil, a naphthene process oil, or the like can be used. Examples of the vegetable oils and fats include castor oil, cottonseed oil, linseed oil, rapeseed oil, soybean oil, palm oil, coconut oil, peanut oil, rosin, pine oil, pine tar, tall oil, corn oil, rice oil, beni-flower oil, sesame oil, olive oil, sunflower oil, palm kernel oil, camellia oil, jojoba oil, macadamia nut oil, and tung oil. These may be used alone or in combination of two or more.

Examples of process oil (mineral oil) include products of Idemitsu Kosan Co., Ltd., Sankyo Yuka Kogyo Co., Ltd., Japan Energy Co., Ltd., Olisoy Co., Ltd., H & R Co., Ltd., Toyokuni Seiyu Co., Ltd., Showa Shell Sekiyu Co., Ltd., and Fuji Kosan Co., Ltd.

The liquid rubber mentioned as the softener is a polymer in a liquid state at room temperature (25° C.) and is a polymer having a monomer similar to that of solid rubber as a constituent element. Examples of the liquid rubber include farnesene-based polymers, liquid diene-based polymers, and hydrogenated additives thereof.

The farnesene-based polymer is a polymer obtained by polymerizing farnesene, and has a structural unit based on farnesene. Farnesene includes isomers such as α-farnesene ((3E, 7E)-3,7,11-trimethyl-1,3,6,10-dodecatetraene) and 8-farnesene (7,11-dimethyl-3-methylene-1, 6,10-dodecatorien).

The farnesene-based polymer may be a homopolymer of farnesene (farnesene homopolymer) or a copolymer of farnesene and a vinyl monomer (farnesene-vinyl monomer copolymer).

Examples of the liquid diene polymer include a liquid styrene-butadiene copolymer (liquid SBR), a liquid butadiene polymer (liquid BR), a liquid isoprene polymer (liquid IR), and a liquid styrene isoprene copolymer (liquid SIR).

The liquid diene polymer has a polystyrene-equivalent weight average molecular weight (Mw) measured by gel permeation chromatography (GPC) of, for example, more than 1.0×10³ and less than 2.0×10⁵. In the present specification, Mw of the liquid diene polymer is a polystyrene conversion value measured by gel permeation chromatography (GPC).

As the liquid rubber, for example, products of Kuraray Co., Ltd. and Clay Valley Co., Ltd. can be used.

(c) Resin Component

The rubber composition preferably contains a resin component, if necessary. The resin component may be solid or liquid at room temperature, and examples of specific resin components include styrene resin, coumarone resin, terpene resin, C5 resin, C9 resin, C5C9 resin, acrylic resin, and the like. Two or more kinds of the resin component may be used in combination. The content of the resin component with respect to 100 parts by mass of the rubber component is preferably more than 2 parts by mass and less than 45 parts by mass, and more preferably less than 30 parts by mass.

The styrene resin is a polymer using a styrene monomer as a constituent monomer, and examples thereof include a polymer obtained by polymerizing a styrene monomer as a main component (50% by mass or more). Specifically, it includes homopolymers obtained by individually polymerizing styrene monomers (styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-methoxystyrene, p-tert-butylstyrene, p-phenylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, etc.), copolymers obtained by copolymerizing two or more styrene monomers, and, in addition, copolymers obtained by copolymerizing a styrene monomer and other monomers that can be copolymerized with the styrene monomer.

Examples of the other monomers include acrylonitriles such as acrylonitrile and methacrylate; unsaturated carboxylic acids such as acrylic acid and methacrylic acid; unsaturated carboxylic acid esters such as methyl acrylate and methyl methacrylate; dienes such as chloroprene, butadiene, and isoprene, olefins such as 1-butene and 1-pentene; and a, 8-unsaturated carboxylic acids such as maleic anhydride and acid anhydrides thereof.

As the coumarone-based resin, coumarone-indene resin is preferably used. Coumarone-indene resin is a resin containing coumarone and indene as monomer components constituting the skeleton (main chain) of the resin. Examples of the monomer component contained in the skeleton other than coumarone and indene include styrene, α-methylstyrene, methylindene, and vinyltoluene.

The content of the coumarone-indene resin is, for example, more than 1.0 part by mass and less than 50.0 parts by mass with respect to 100 parts by mass of the rubber component.

The hydroxyl value (OH value) of the coumarone-indene resin is, for example, more than 15 mgKOH/g and less than 150 mgKOH/g. The OH value is the amount of potassium hydroxide required to neutralize acetic acid bonded to a hydroxyl group when 1 g of the resin is acetylated, and is expressed in milligrams. It is a value measured by potentiometric titration method (JIS K 0070: 1992).

The softening point of the coumarone-indene resin is, for example, higher than 30° C. and lower than 160° C. The softening point is the temperature at which the ball drops when the softening point defined in JIS K 6220-1: 2001 is measured by a ring-ball type softening point measuring device.

Examples of the terpene resins include polyterpenes, terpene phenols, and aromatic-modified terpene resins. Polyterpene is a resin obtained by polymerizing a terpene compound and a hydrogenated product thereof. The terpene compound is a hydrocarbon having a composition of (C₅H₈)_(n) or an oxygen-containing derivative thereof, which is a compound having a terpene classified as monoterpenes (C₁₀H₁₆), sesquiterpenes (C₁₅H₂₄), diterpenes (C₂₀H₃₂), etc. as the basic skeleton. Examples thereof include α-pinene, β-pinene, dipentene, limonene, myrcene, alloocimene, osimene, α-phellandrene, α-terpinene, γ-terpinene, terpinolene, 1,8-cineol, 1,4-cineol, α-terpineol, 8-terpineol, and γ-terpineol.

Examples of the polyterpene include terpene resins such as α-pinene resin, β-pinene resin, limonene resin, dipentene resin, and β-pinene/limonene resin, which are made from the above-mentioned terpene compound, as well as hydrogenated terpene resin obtained by hydrogenating the terpene resin. Examples of the terpene phenol include a resin obtained by copolymerizing the above-mentioned terpene compound and the phenol compound, and a resin obtained by hydrogenating above-mentioned resin. Specifically, a resin obtained by condensing the above-mentioned terpene compound, the phenol compound and the formalin can be mentioned. Examples of the phenol compound include phenol, bisphenol A, cresol, and xylenol. Examples of the aromatic-modified terpene resin include a resin obtained by modifying a terpene resin with an aromatic compound, and a resin obtained by hydrogenating above-mentioned resin. The aromatic compound is not particularly limited as long as it is a compound having an aromatic ring, and examples thereof include phenol compounds such as phenol, alkylphenol, alkoxyphenol, and unsaturated hydrocarbon group-containing phenol; naphthol compounds such as naphthol, alkylnaphthol, alkoxynaphthol, and unsaturated hydrocarbon group-containing naphthols; styrene derivatives such as styrene, alkylstyrene, alkoxystyrene, unsaturated hydrocarbon group-containing styrene; coumarone, and indene.

The C5 resin refers to a resin obtained by polymerizing a C5 fraction. Examples of the C5 fraction include petroleum fractions having 4 to 5 carbon atoms such as cyclopentadiene, pentene, pentadiene, and isoprene. As the C5-based petroleum resin, a dicyclopentadiene resin (DCPD resin) is preferably used.

The C9 resin refers to a resin obtained by polymerizing a C9 fraction, and may be hydrogenated or modified. Examples of the C9 fraction include petroleum fractions having 8 to 10 carbon atoms such as vinyltoluene, alkylstyrene, indene, and methyl indene. As the specific examples, a coumarone-indene resin, a coumarone resin, an indene resin, and an aromatic vinyl resin are preferably used. As the aromatic vinyl resin, a homopolymer of α-methylstyrene or styrene or a copolymer of α-methylstyrene and styrene is preferable because it is economical, easy to process, and excellent in heat generation. A copolymer of α-methylstyrene and styrene is more preferred. As the aromatic vinyl-based resin, for example, those commercially available from Clayton, Eastman Chemical, etc. can be used.

The C5C9 resin refers to a resin obtained by copolymerizing the C5 fraction and the C9 fraction, and may be hydrogenated or modified. Examples of the C5 fraction and the C9 fraction include the above-mentioned petroleum fraction. As the C5C9 resin, for example, those commercially available from Tosoh Corporation, LUHUA, etc. can be used.

The acrylic resin is not particularly limited, but for example, a solvent-free acrylic resin can be used.

As the solvent-free acrylic resin, a (meth) acrylic resin (polymer) synthesized by a high-temperature continuous polymerization method (high-temperature continuous lump polymerization method (a method described in U.S. Pat. No. 4,414,370 B, JP 84-6207 A, JP 93-58805 B, JP 89-313522 A, U.S. Pat. No. 5,010,166 B, Toa Synthetic Research Annual Report TREND2000 No. 3 p 42-45, and the like) without using polymerization initiators, chain transfer agents, organic solvents, etc. as auxiliary raw materials as much as possible, can be mentioned. In the present disclosure, (meth) acrylic means methacrylic and acrylic.

Examples of the monomer component constituting the acrylic resin include (meth) acrylic acid, and (meth) acrylic acid derivatives such as (meth) acrylic acid ester (alkyl ester, aryl ester, aralkyl ester, etc.), (meth) acrylamide, and (meth) acrylamide derivative.

In addition, as the monomer component constituting the acrylic resin, aromatic vinyl compounds such as styrene, α-methylstyrene, vinyltoluene, vinylnaphthalene, divinylbenzene, trivinylbenzene, divinylnaphthalene, and the like may be used, together with (meth) acrylic acid or (meth) acrylic acid derivative.

The acrylic resin may be a resin composed of only a (meth) acrylic component or a resin also having a component other than the (meth) acrylic component. Further, the acrylic resin may have a hydroxyl group, a carboxyl group, a silanol group, or the like.

As the resin component, for example, a product of Maruzen Petrochemical Co., Ltd., Sumitomo Bakelite Co., Ltd., Yasuhara Chemical Co., Ltd., Toso Co., Ltd., Rutgers Chemicals Co., Ltd., BASF Co., Ltd., Arizona Chemical Co., Ltd., Nitto Chemical Co., Ltd., Co., Ltd., Nippon Catalyst Co., Ltd., JX Energy Co., Ltd., Arakawa Chemical Industry Co., Ltd., Taoka Chemical Industry Co., Ltd. can be used.

(d) Anti-Aging Agent

The rubber composition preferably contains an anti-aging agent. Content of the anti-aging agent is, for example, more than 1 part by mass and less than 10 parts by mass, and more preferably 6.5 parts by mass or more, with respect to 100 parts by mass of the rubber component.

Examples of the antiaging agent include naphthylamine-based antiaging agents such as phenyl-α-naphthylamine; diphenylamine-based antiaging agents such as octylated diphenylamine and 4,4′-bis (α,α′-dimethylbenzyl) diphenylamine; p-phenylenediamine-based anti-aging agent such as N-isopropyl-N′-phenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine, and N,N′-di-2-naphthyl-p-phenylenediamine; quinoline-based anti-aging agent such as a polymer of 2,2,4-trimethyl-1,2-dihydroquinolin; monophenolic anti-aging agents such as 2,6-di-t-butyl-4-methylphenol, styrenated phenol; bis, tris, polyphenolic anti-aging agents such as tetrakis-[methylene-3-(3′,5′-di-t-butyl-4′-hydroxyphenyl)propionate]methane. These may be used alone or in combination of two or more.

As the anti-aging agent, for example, products of Seiko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Ouchi Shinko Chemical Industry Co., Ltd., Flexsys Co., Ltd., etc. can be used.

(e) Stearic Acid

The rubber composition may contain stearic acid. Content of stearic acid is, for example, more than 0.5 parts by mass and less than 10.0 parts by mass, and more preferably 3 parts by mass or more, with respect to 100 parts by mass of the rubber component. As the stearic acid, conventionally known ones can be used, and, for example, products of NOF Corporation, NOF Corporation, Kao Corporation, Fuji film Wako Pure Chemical Industries, Ltd., and Chiba Fatty Acid Co., Ltd., etc. can be used.

(f) Zinc Oxide

The rubber composition may contain zinc oxide. Content of zinc oxide is, for example, more than 0.5 parts by mass and less than 10 parts by mass, and more preferably 4.5 parts by mass or more, with respect to 100 parts by mass of the rubber component. As the zinc oxide, conventionally known ones can be used, for example, products of Mitsui Metal Mining Co., Ltd., Toho Zinc Co., Ltd., Hakusui Tech Co., Ltd., Shodo Chemical Industry Co., Ltd., Sakai Chemical Industry Co., Ltd., etc. can be used.

(g) Wax

The rubber composition preferably contains wax. Content of the wax is, for example, 0.5 to 20 parts by mass, preferably 1.0 to 15 parts by mass, and more preferably 1.5 to 10.0 parts by mass with respect to 100 parts by mass of the rubber component. It is further preferably 2.0 parts by mass or more.

The wax is not particularly limited, and examples thereof include petroleum waxes such as paraffin wax and microcrystalline wax; natural waxes such as plant wax and animal wax; and synthetic waxes such as a polymer of ethylene or propylene. These may be used alone or in combination of two or more.

As the wax, for example, products of Ouchi Shinko Chemical Industry Co., Ltd., Nippon Seiro Co., Ltd., and Seiko Kagaku Co., Ltd. can be used.

(h) Crosslinking Agent and Vulcanization Accelerator

The rubber composition preferably contains a cross-linking agent such as sulfur. Content of the cross-linking agent is, for example, more than 0.1 part by mass and less than 10.0 parts by mass, and more preferably 2 parts by mass or more, with respect to 100 parts by mass of the rubber component.

Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, and soluble sulfur, which are commonly used in the rubber industry. These may be used alone or in combination of two or more.

As the sulfur, for example, products of Tsurumi Chemical Industry Co., Ltd., Karuizawa Sulfur Co., Ltd., Shikoku Chemicals Corporation, Flexsys Co., Ltd., Nippon Kanryu Kogyo Co., Ltd., Hosoi Chemical Industry Co., Ltd., etc. can be used.

Examples of the cross-linking agent other than sulfur include vulcanizing agents containing a sulfur atom such as Tackirol V200 manufactured by Taoka Chemical Industry Co., Ltd., DURALINK HTS (1,6-hexametdihylene-sodium dithiosulfate dihydrate) manufactured by Flexsys, and KA9188 (1,6-bis (N, N′-dibenzylthiocarbamoyldithio) hexane) manufactured by Lanxess; and organic peroxides such as dicumylperoxide.

The rubber composition preferably contains a vulcanization accelerator. Content of the vulcanization accelerator is, for example, more than 0.3 parts by mass and less than 10.0 parts by mass, and more preferably 1 part by mass or more, and further preferably 1.5 parts by mass or more with respect to 100 parts by mass of the rubber component.

Examples of the vulcanization accelerator include

-   -   thiazole-based vulcanization accelerators such as         2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide, and         N-cyclohexyl-2-benzothiadylsulfenamide;     -   thiuram-based vulcanization accelerators such as         tetramethylthiuram disulfide (TMTD), tetrabenzyltiuram disulfide         (TBzTD), and tetrakis (2-ethylhexyl) thiuram disulfide (TOT-N);     -   sulfenamide-based vulcanization accelerators such as         N-cyclohexyl-2-benzothiazolesulfenamide,         N-t-butyl-2-benzothiazolyl sulfenamide,         N-oxyethylene-2-benzothiazolesulfenamide,         N-oxyethylene-2-benzothiazolesulfenamide, and N,         N′-diisopropyl-2-benzothiazolesulfenamide; and guanidine-based         vulcanization accelerators such as diphenylguanidine,         di-ortho-tolylguanidine and ortho-tolylbiguanidine. These may be         used alone or in combination of two or more.

(i) Other

In addition to the above components, the rubber composition may further contain additives generally used in the tire industry, such as fatty acid metal salts, carboxylic acid metal salts, and organic peroxides. Content of these additives is, for example, more than 0.1 part by mass and less than 200 parts by mass with respect to 100 parts by mass of the rubber component.

2. Production of Rubber Composition for Forming the Side Portion

The rubber composition is produced by a general method, for example, a manufacturing method including a base kneading step of kneading a rubber component with a filler such as carbon black, and a finish kneading step of kneading the kneaded product obtained in the base kneading step and a cross-linking agent.

The kneading can be performed using a known (sealed) kneader such as a banbury mixer, a kneader, or an open roll.

The kneading temperature in the base kneading step is, for example, higher than 50° C. and lower than 200° C., and the kneading time is, for example, more than 30 seconds and less than 30 minutes. In the base kneading process, in addition to the above components, compounding agents conventionally used in the rubber industry, such as softeners such as oil, stearic acid, zinc oxide, antiaging agents, waxes, and vulcanization accelerators, may be appropriately added and kneaded as needed.

In the finish kneading step, the kneaded product obtained in the base kneading step and the cross-linking agent are kneaded. The kneading temperature in the finish kneading step is, for example, above room temperature and lower than 80° C., and the kneading time is, for example, more than 1 minute and less than 15 minutes. In the finish kneading step, in addition to the above components, a vulcanization accelerator, zinc oxide and the like may be appropriately added and kneaded as needed.

3. Tire Manufacturing

The tire of the present disclosure is manufactured by a usual method using an unvulcanized rubber composition obtained through the finish kneading step. That is, the unvulcanized rubber composition is extruded according to the shape of side wall, and is molded together with other tire members by a normal method on a tire molding machine to produce an unvulcanized tire.

Specifically, on the molded drum, the inner liner as a member to ensure the air-tightness of the tire, the carcass as a member to withstand the load, impact and filling air pressure received by the tire, the belt as a member to strongly tighten the carcass to increase the rigidity of the tread, and the like are wound, both ends of the carcass are fixed to both side edges, a bead part as a member for fixing the tire to the rim is arranged, and they are formed into a toroid shape. Then the tread is pasted on the center of the outer circumference, and the sidewall portion is pasted on the radially outer side to form a side portion, and an unvulcanized tire is prodeced.

In the present embodiment, it is preferable to provide with an inclined belt layer that extends at an angle of 15° to 30° with respect to the tire circumferential direction, as the belt. As a result, the durability of the tire is ensured while the rigidity of the tread can be sufficiently maintained. Further, since it can be restrained in the circumferential direction, it becomes easy to suppress the growth of the outer diameter.

Then, the produced unvulcanized tire is heated and pressed in a vulcanizer to obtain a tire. The vulcanization step can be carried out by applying a known vulcanization means. The vulcanization temperature is, for example, higher than 120° C. and lower than 200° C., and the vulcanization time is, for example, more than 5 minutes and less than 15 minutes.

At this time, the tire is formed into a shape that satisfies the above-mentioned (formula 1) and (formula 2) when the tire is installed on a standardized rim and the internal pressure is set to 250 kPa.

Specific tires that can satisfy the above (formula 1) and (formula 2) include tires with size notation of 145/60R18, 145/60R19, 155/55R18, 155/55R19, 155/70R17, 155/70R19, 165/55R20, 165/55R21, 165/60R19, 165/65R19, 165/70R18, 175/55R19, 175/55R20, 175/55R22, 175/60R18, 185/55R19, 185/60R20, 195/50R20, 195/55R20, etc.

In the present embodiment, the tires that can satisfy (formula 1) and (formula 2) are preferably applied to pneumatic tires for passenger cars, and satisfying the above formulas can contribute more favorably to solve the problem in the present disclosure of providing a pneumatic tire with reduced rolling resistance and excellent durability during high-speed running.

EXAMPLES

Hereinafter, the present disclosure will be described in more specific with reference to Examples.

Experiment 1

In this experiment, 175 size tires were prepared and evaluated.

1. Manufacture of Rubber Compositions for Forming Side Portion

A rubber composition for forming side portion was produced.

(1) Compounding Material

First, each compounding material shown below was prepared.

(a) Rubber Component

-   -   (a-1) NR: TSR20     -   (a-2) BR-1: UBEPOL-BR150B manufactured by Ube Industries, Ltd.         (cis content: 97% by mass)     -   (a-3) BR-2: Nipol-BR1250H manufactured by Nippon Zeon Co., Ltd.         (tin terminal modified BR, cis content: 40% by mass)     -   (a-4) BR-3: UBEPOL VCR617 manufactured by Ube Industries, Ltd.         (cis content: 98% by mass)

(b) Compounding Materials Other than Rubber Components

-   -   (b-1) Carbon black: Show Black N550 manufactured by Cabot Japan         Co., Ltd. (N₂SA: 42m2/g)     -   (b-2) Oil: Process X-140 manufactured by Japan Energy Co., Ltd.     -   (b-3) Stearic acid: stearic acid “Tsubaki” manufactured by NOF         Corporation     -   (b-4) Zinc oxide: zinc oxide No. 1 manufactured by Mitsui Mining         & Smelting Co., Ltd.     -   (b-5) Wax: Sannok wax manufactured by Ouchi Shinko Chemical         Industry Co., Ltd.     -   (b-6) Antiaging agent-1: Nocrac 6C manufactured by Ouchi Shinko         Chemical Industry Co., Ltd.         (N-phenyl-N′-(1,3-dimethylbutyl)-p-phenylenediamine)     -   (b-7) Anti-aging agent-2: Antage RD manufactured by Kawaguchi         Chemical Industry Co., Ltd.         (2,2,4-trimethyl-1,2-dihydroquinoline)     -   (b-8) Cross-linking agent and vulcanization accelerator

Sulfur: powdered sulfur manufactured by Tsurumi Chemical Industry Co., Ltd.

Vulcanization accelerator: Nocceler NS manufactured by Ouchi Shinko Chemical Industry Co., Ltd. (N-tert-butyl-2-benzothiazolylsulfenamide)

(2) Production of Rubber Composition for Forming Side Portion

In accordance with the formulation shown in Table 1 and Table 2, materials other than sulfur and the vulcanization accelerator were kneaded under the conditions of 150° C. for 5 minutes using a banbury mixer to obtain a kneaded product. Each compounding amount is a mass part.

Next, sulfur and a vulcanization accelerator were added to the obtained kneaded product, and the mixture was kneaded at 80° C. for 5 minutes using an open roll to obtain a rubber composition for forming side portion.

2. Tire Manufacturing

Using the obtained rubber composition, a side member was formed to have a thickness S (mm) shown in Tables 1 and 2, and was bonded together with other tire members to form an unvulcanized tire, which is then press-vulcanized for 10 minutes under the condition of 170° C. to produce each test tire having a size of 175 type (Example 1-1 to Example 1-5 and Comparative Example 1-1 to Comparative Example 1-5).

3. Parameter Calculation

After that, the outer diameter Dt (mm), the cross-sectional width Wt (mm), the cross-sectional height Ht (mm), and the aspect ratio (%) of each test tire were obtained, and the virtual volume V (mm³) was calculated. At the same time, a rubber test piece for viscoelasticity measurement was produced by cutting out from the rubber layer of the side portion of each test tire in a length 20 mm×width 4 mm×thickness 1 mm so that the tire circumferential direction was the long side. For each rubber test piece, tan δ (70° C. tan δ) was measured under the conditions of 70° C., frequency 10 Hz, initial strain 5%, and dynamic strain 1% using an Eplexor series manufactured by GABO Co., Ltd. The results are shown in Tables 1 and 2.

Then, (Dt−2×Ht), (Dt²×π/4)/Wt, (V+1.5×10⁷)/Wt, (V+2.0×10⁷)/Wt, (V+2.5×10⁷)/Wt, and 70° C. tan δ×Wt were determined. The results are shown in Tables 1 and 2.

5. Performance Evaluation Test (1) Evaluation of Rolling Resistance at High-Speed Running

Each test tire was installed on all wheels of the vehicle (domestic FF vehicle, displacement 2000 cc), filled with air so that the internal pressure became 250 kPa, and then driven on a dry road surface test course at a speed of 100 km/h. After making a 10 km lap, the accelerator was released, and the distance from when the accelerator was turned off until the vehicle stopped was measured as the rolling resistance at high-speed running.

Next, the result in Comparative Example 1-5 was set to as 100, and the results were indexed based on the following formula to relatively evaluate the rolling resistance at high-speed running. The larger the value, the longer the distance from when the accelerator is turned off until the vehicle stops and the smaller the rolling resistance in the steady state, and showing excellent fuel efficiency.

Rolling resistance=[(Result of test tire)/(Result of Comparative Example 1-5)]×100

(2) Evaluation of Durability Performance

After installing each test tire on all wheels of the vehicle (domestic FF vehicle, displacement 2000 cc) and filling it with air so that the internal pressure becomes 250 kPa, a driving 10 laps at a speed of 50 km/h, followed by climbing onto the unevenness provided on the road surface at a speed of 80 km/h was repeated on the test course on a dry road surface in an overloaded state. Thereafter, the lap was performed again at a speed of 50 km/h and then the speed was gradually increased to measure the speed at the time when the driver felt an abnormality.

Next, the result in Comparative Example 1-5 was set to as 100, and the durability performance was relatively evaluated by indexing based on the following formula. The larger the value, the better the durability.

Durability=[(Result of test tire)/(Result of Comparative Example 1-5)]×100

(3) Comprehensive Evaluation

The evaluation results of (1) and (2) above were totaled to obtain a comprehensive evaluation.

(4) Evaluation Result

The results of each evaluation are shown in Tables 1 and 2.

Example No. 1-1 1-2 1-3 1-4 1-5 SIZE 175/ 175/ 175/ 175/ 175/ 40R21 40R21 40R21 50R20 60R19 (Formulation) NR 40 40 40 40 40 BR 1 BR 2 30 30 30 30 30 BR 3 30 30 30 30 30 Carbon black 45 40 40 45 45 Oil 15 15 15 15 15 Stearic acid 3 3 3 3 3 Zinc oxide 4.5 4.5 4.5 4.5 4.5 Wax 2 2 2 2 2 Anti-aging 4.5 4.5 4.5 4.5 4.5 agent-1 Anti-aging 2 2 2 2 2 agent-2 Sulfur 2 2 2 2 2 Vulcanization 1 1.5 1.5 1 1 accelerator (Parameter) 70° C. tanδ 0.11 0.07 0.07 0.11 0.11 S (mm) 3 3 1.5 3 3 Dt (mm) 674 673 672 684 692 V (mm³) 23672177 23206160 23136067 30111710 34196412 Wt (mm) 176 175 177 181 178 Ht(mm) 71 70 69 89 104 Dt − 2 × 532 533 534 506 484 Ht(mm) (Dt² × π/4)/Wt 2027 2033 2004 2030 2113 (V + 1.5 × 219728 218321 215458 249236 276384 10⁷)/Wt (V + 2.0 × 248137 246892 243707 276860 304474 10⁷)/Wt (V + 2.5 × 276546 275464 271955 304485 332564 10⁷)/Wt Aspect ratio 40 40 39 49 58 (%) 70° C. tanδ × 44385 27847 13725 54900 63398 V/Wt × S (Evaluation result) Rolling 116 120 132 112 110 resistance at high-speed running Durability 124 128 136 120 112 Comprehensive 240 248 268 232 222 evaluation

TABLE 2 Comparative example No. 1-1 1-2 1-3 1-4 1-5 SIZE 175/ 175/ 175/ 175/ 175/ 80R14 60R19 80R14 80R14 80R14 (Formulation) NR 40 40 40 40 40 BR 1 60 60 60 BR 2 30 30 BR 3 30 30 Carbon black 60 60 60 45 40 Oil 15 15 15 15 15 Stearic acid 3 3 3 3 3 Zinc oxide 4.5 4.5 4.5 4.5 4.5 Wax 2 2 2 2 2 Anti-aging 4.5 4.5 4.5 4.5 4.5 agent-1 Anti-aging 2 2 2 2 2 agent-2 Sulfur 2 2 2 2 2 Vulcanization 1 1 1 1 1.5 accelerator (Parameter) 70° C. tanδ 0.2 0.2 0.2 0.11 0.07 S (mm) 5 5 3 5 3 Dt (mm) 636 693 635 637 636 V (mm³) 38414424 34599284 38317377 38669035 38414424 Wt (mm) 177 177 176 176 177 Ht(mm) 139 106 140 141 139 Dt − 2 × 358 481 355 355 358 Ht(mm) (Dt² × π/4)/Wt 1795 2131 1799 1811 1795 (V + 1.5 × 301776 280222 302940 304938 301776 10⁷)/Wt (V + 2.0 × 330025 308471 331349 333347 330025 10⁷)/Wt (V + 2.5 × 358274 336719 359758 361756 358274 10⁷)/Wt Aspect ratio 79 60 80 80 79 (%) 70° C. tanδ × 217031 195476 130627 120841 45576 V/Wt × S (Evaluation result) Rolling 94 98 94 96 100 resistance at high speed running Durability 90 96 96 92 100 Comprehensive 184 194 190 188 200 evaluation

Experiment 2

In this experiment, 195 size tires were prepared and evaluated.

After producing the test tires of Examples 2-1 to 2-5 and Comparative Examples 2-1 to 2-5 shown in Tables 3 and 4 in the same manner as in Experiment 1, each parameter was calculated by performing the same procedure. Then, in the same manner, a performance evaluation test was conducted and evaluated. In this experiment, the result in Comparative Example 2-5 was set as 100 for evaluation. The results of each evaluation are shown in Tables 3 and 4.

TABLE 3 Example No. 2-1 2-2 2-3 2-4 2-5 SIZE 195/ 195/ 195/ 195/ 195/ 40R20 40R20 40R20 50R19 60R18 (Formulation) NR 40 40 40 40 40 BR 1 BR 2 30 30 30 30 30 BR 3 30 30 30 30 30 Carbon black 45 40 40 45 45 Oil 15 15 15 15 15 Stearic acid 3 3 3 3 3 Zinc oxide 4.5 4.5 4.5 4.5 4.5 Wax 2 2 2 2 2 Anti-aging 4.5 4.5 4.5 4.5 4.5 agent-1 Anti-aging 2 2 2 2 2 agent-2 Sulfur 2 2 2 2 2 Vulcanization 1 1.5 1.5 1 1 accelerator (Parameter) 70° C. tanδ 0.11 0.07 0.07 0.11 0.11 S (mm) 3 3 1.5 3 3 Dt (mm) 665 663 664 680 691 V (mm³) 29087378 28526824 28431992 35417448 42618582 Wt (mm) 200 199 198 196 202 Ht(mm) 79 78 78 99 117 Dt − 2 × 507 507 508 482 457 Ht(mm) (Dt² × π/4)/Wt 1737 1735 1749 1853 1856 (V + 1.5 × 220437 218728 219353 257232 285241 10⁷)/Wt (V + 2.0 × 245437 243853 244606 282742 309993 10⁷)/Wt (V + 2.5 × 270437 268979 269859 308252 334745 10⁷)/Wt Aspect ratio 40 39 39 51 58 (%) 70° C. tanδ × 47994 30104 15078 59631 69624 V/Wt × S (Evaluation result) Rolling 118 122 126 116 118 resistance at high-speed running Durability 126 132 134 118 110 Comprehensive 244 254 260 234 228 evaluation

TABLE 4 Comparative example No. 2-1 2-2 2-3 2-4 2-5 SIZE 195/ 195/ 195/ 195/ 195/ 65R17 40R20 65R17 65R17 65R17 (Formulation) NR 40 40 40 40 40 BR 1 60 60 60 BR 2 30 30 BR 3 30 30 Carbon black 60 60 60 45 40 Oil 15 15 15 15 15 Stearic acid 3 3 3 3 3 Zinc oxide 4.5 4.5 4.5 4.5 4.5 Wax 2 2 2 2 2 Anti-aging 4.5 4.5 4.5 4.5 4.5 agent-1 Anti-aging 2 2 2 2 2 agent-2 Sulfur 2 2 2 2 2 Vulcanization 1 1 1 1 1.5 accelerator (Parameter) 70° C. tanδ 0.2 0.2 0.2 0.11 0.07 S (mm) 5 5 3 5 3 Dt (mm) 686 664 686 685 687 V (mm³) 44829249 28719183 44877023 44971685 44957448 Wt (mm) 201 200 200 202 200 Ht(mm) 127 78 128 127 128 Dt − 2 × 432 508 430 431 431 Ht(mm) (Dt² × π/4)/Wt 1839 1731 1848 1824 1853 (V + 1.5 × 297658 218596 299385 296890 299787 10⁷)/Wt (V + 2.0 × 322534 243596 324385 321642 324787 10⁷)/Wt (V + 2.5 × 347409 268596 349385 346394 349787 10⁷)/Wt Aspect ratio 63 39 64 63 64 (%) 70° C. tanδ × 223031 143596 134631 122448 47205 V/Wt × S (Evaluation result) Rolling 96 98 96 98 100 resistance at high speed running Durability 90 96 96 94 100 Comprehensive 186 194 192 192 200 evaluation

Experiment 3

In this experiment, 225 size tires were prepared and evaluated.

After producing the test tires of Examples 3-1 to 3-5 and Comparative Examples 3-1 to 3-5 shown in Tables 5 and 6 in the same manner as in Experiment 1, each parameter was calculated by performing the same procedure. Then, in the same manner, a performance evaluation test was conducted and evaluated. In this experiment, the result in Comparative Example 3-5 was set as 100 for evaluation. The results of each evaluation are shown in Tables 5 and 6.

TABLE 5 Example No. 3-1 3-2 3-3 3-4 3-5 SIZE 225/ 225/ 225/ 225/ 225/ 35R22 35R22 35R22 50R20 40R21 (Formulation) NR 40 40 40 40 40 BR 1 BR 2 30 30 30 30 30 BR 3 30 30 30 30 30 Carbon black 45 40 40 45 45 Oil 15 15 15 15 15 Stearic acid 3 3 3 3 3 Zinc oxide 4.5 4.5 4.5 4.5 4.5 Wax 2 2 2 2 2 Anti-aging 4.5 4.5 4.5 4.5 4.5 agent-1 Anti-aging 2 2 2 2 2 agent-2 Sulfur 2 2 2 2 2 Vulcanization 1 1.5 1.5 1 1 accelerator (Parameter) 70° C. tanδ 0.11 0.07 0.07 0.11 0.11 S (mm) 3 3 1.5 3 3 Dt (mm) 716 718 717 734 713 V (mm³) 36203610 37040131 35785417 50043281 40161995 Wt (mm) 229 231 226 227 228 Ht(mm) 79 80 79 113 90 Dt − 2 × 558 558 559 508 533 Ht(mm) (Dt² × π/4)/Wt 1758 1753 1787 1864 1751 (V + 1.5 × 223597 225282 224714 286534 241939 10⁷)/Wt (V + 2.0 × 245431 246927 246838 308561 263868 10⁷)/Wt (V + 2.5 × 267265 268572 268962 330587 285798 10⁷)/Wt Aspect ratio 34 35 35 50 39 (%) 70° C. tanδ × 52171 33673 16626 72750 58129 V/Wt × S (Evaluation result) Rolling 108 116 126 110 114 resistance at high-speed running Durability 126 130 128 122 114 Comprehensive 234 246 254 232 228 evaluation

TABLE 6 Comparative example No. 3-1 3-2 3-3 3-4 3-5 SIZE 225/ 225/ 225/ 225/ 225/ 60R20 50R20 60R20 60R20 60R20 (Formulation) NR 40 40 40 40 40 BR 1 60 60 60 BR 2 30 30 BR 3 30 30 Carbon black 60 60 60 45 40 Oil 15 15 15 15 15 Stearic acid 3 3 3 3 3 Zinc oxide 4.5 4.5 4.5 4.5 4.5 Wax 2 2 2 2 2 Anti-aging 4.5 4.5 4.5 4.5 4.5 agent-1 Anti-aging 2 2 2 2 2 agent-2 Sulfur 2 2 2 2 2 Vulcanization 1 1 1 1 1.5 accelerator (Parameter) 70° C. tanδ 0.2 0.2 0.2 0.11 0.07 S (mm) 5 5 3 5 3 Dt (mm) 778 736 732 735 777 V (mm³) 62176957 51904024 50611309 51375765 62080258 Wt (mm) 228 233 232 231 228 Ht(mm) 135 114 112 114 135 Dt − 2 × 508 508 508 507 507 Ht(mm) (Dt² × π/4)/Wt 2085 1826 1814 1837 2080 (V + 1.5 × 338495 287142 282807 287341 338071 10⁷)/Wt (V + 2.0 × 360425 308601 304359 308986 360001 10⁷)/Wt (V + 2.5 × 382355 330060 325911 330631 381931 10⁷)/Wt Aspect ratio 59 49 48 49 59 (%) 70° C. tanδ × 272706 222764 130891 122323 57179 V/Wt × S (Evaluation result) Rolling 96 98 96 94 100 resistance at high-speed running Durability 90 96 96 92 100 Comprehensive 186 194 192 186 200 evaluation

Summary of Experiments 1 to 3

From the results of Experiments 1 to 3 (Tables 1 to 6), for tires of any size, 175 size, 195 size, 225 size, it turns out that it is possible to provide a pneumatic tire in which the rolling resistance at high-speed running is sufficiently reduced and the durability is sufficiently improved, when the above (formula 1) and (formula 2) are satisfied.

Then, it turns out that, by satisfying each of the requirements specified in claim 2 and thereafter, it is possible to provide a tire with further improved rolling resistance and durability at high-speed running.

On the other hand, when either (formula 1) or (formula 2) is not satisfied, the rolling resistance at high-speed running cannot be sufficiently reduced, and the durability cannot be sufficiently improved.

Experiment 4

Next, three types of tires (Examples 4-1 to 4-3), in which the relationship between the virtual volume V and the cross-sectional width Wt did not differ significantly, were produced with the same formulation and evaluated in the same manner. Here, in addition to the evaluation of rolling resistance and durability during high-speed running, the ride comfort was also evaluated.

Specifically, each test tire was installed on all wheels of the vehicle (domestic FF vehicle, displacement 2000 cc), filled with air so that the internal pressure became 250 kPa, and then driven on a dry road surface test course. The driver sensory-tested the ride comfort on a 5-point scale when the vehicle has driven 10 km at a speed of 100 km/h. After summing up the evaluations by 20 drivers, the evaluation was indexed based on the following formula, with the total score in Example 4-3 being 100, and the riding comfort was relatively evaluated. A larger value indicates better riding comfort.

Ride comfort=[(Total evaluation score of test tire)/(Total evaluation score of Example 4-3)]×100

Then, as in Experiments 1 to 3, each evaluation result was totaled to obtain a comprehensive evaluation. Table 7 shows the results of each evaluation.

TABLE 7 Example No. 4-1 4-2 4-3 SIZE 175/55R18 195/50R19 225/45R20 (Formulation) NR 40 40 40 BR 1 BR 2 30 30 30 BR 3 30 30 30 Carbon black 45 45 45 Oil 15 15 15 Stearic acid 3 3 3 Zinc oxide 4.5 4.5 4.5 Wax 2 2 2 Anti-aging agent-1 4.5 4.5 4.5 Anti-aging agent-2 2 2 2 Sulfur 2 2 2 Vulcanization 1 1 1 accelerator (Parameter) 70° C. tanδ 0.11 0.11 0.11 S (mm) 1.5 1.5 1.5 Dt (mm) 649 679 710 V (mm³) 30354118 35954077 43478150 Wt (mm) 182 201 225 Ht(mm) 96 98 101 Dt − 2 × Ht(mm) 457 483 508 (Dt² × π/4)/Wt 1818 1801 1760 (V + 1.5 × 10⁷)/Wt 249198 253503 259903 (V + 2.0 × 10⁷)/Wt 276671 278378 282125 (V + 2.5 × 10⁷)/Wt 304144 303254 304347 Aspect ratio (%) 53 49 45 70° C. tanδ × V/Wt × S 27519 29515 31884 (Evaluation result) Rolling resistance at 110 106 100 high-speed running Durability 100 104 106 Ride confort 110 106 100 Comprehensive 320 315 306 evaluation

Table 7 shows that, when there is no large difference in the relationship between the virtual volume V and the cross-sectional width Wt, the rolling resistance at high-speed running and durability are both improved, as the cross-sectional width Wt becomes smaller as from less than 205 mm to less than 200 mm, and as the aspect ratio increases. It was also found that the ride comfort was improved.

Although the present disclosure has been described above based on the embodiments, the present disclosure is not limited to the above embodiments. Various modifications can be made to the above embodiments within the same and equal range as the present disclosure.

The present disclosure (1) is;

-   -   a pneumatic tire having a side portion, wherein     -   the thickness S (mm) of the rubber layer radially outside the         carcass of the side portion at the maximum width position of the         tire is 3 mm or less;     -   the loss tangent (70° C. tan δ) of the rubber layer is 0.15 or         less measured under the conditions of 70° C., frequency of 10         Hz, initial strain of 5%, and dynamic strain rate of 1%; and     -   when the cross-sectional width of the tire is Wt (mm), the outer         diameter is Dt (mm), and the volume of the space occupied by the         tire is the virtual volume V (mm³), when the tire is installed         on a standardized rim and the internal pressure is 250 kPa, the         tire satisfies following (formula 1) and (formula 2):

1700≤(Dt ²×π/4)/Wt≤2827.4  (formula 1)

[(V+1.5×10⁷)/Wt]≤2.88×10⁵  (formula 2)

The present disclosure (2) is the pneumatic tire according to the present disclosure (1), wherein the following (formula 3) is satisfied.

[(V+2.0×10⁷)/Wt]≤2.88×10⁵  (formula 3)

The present disclosure (3) is the pneumatic tire according to the present disclosure (2), wherein the following (formula 4) is satisfied.

[(V+2.5×10⁷)/Wt]≤2.88×10⁵  (formula 4)

The present disclosure (4) is the pneumatic tire of any combination of the present disclosures (1) to (3), wherein, when the outer diameter of the tire is Dt (mm) and the cross-sectional height of the tire is Ht (mm) when the tire is installed on a standardized rim and the internal pressure is 250 kPa, (Dt−2×Ht) is 470 (mm) or more.

The present disclosure (5) is the pneumatic tire of any combination of the present disclosures (1) to (4), which has an aspect ratio of 40% or more.

The present disclosure (6) is the pneumatic tire according to the present disclosure (5), which has an aspect ratio of 45% or more.

The present disclosure (7) is the pneumatic tire according to the present disclosure (6), which has an aspect ratio of 47.5% or more.

The present disclosure (8) is the pneumatic tire according to the present disclosure (7), which has an aspect ratio of 50% or more.

The present disclosure (9) is the pneumatic tire of any combination of the present disclosures (1) to (8), wherein the following (formula 5) is satisfied:

70° C. tan δ×(V/Wt)×S≤80000  (formula 5)

The present disclosure (10) is the pneumatic tire according to the present disclosure (9), wherein the following (formula 6) is satisfied:

70° C. tan δ×(V/Wt)×S≤60000  (formula 6)

The present disclosure (11) is the pneumatic tire according to the present disclosure (10), wherein the following (formula 7) is satisfied:

70° C. tan δ×(V/Wt)×S≤40000  (formula 7)

The present disclosure (12) is the pneumatic tire according to the present disclosure (11), wherein the following (formula 8) is satisfied:

70° C. tan δ×(V/Wt)×S≤35000  (formula 8)

The present disclosure (13) is the pneumatic tire of any combination of the present disclosures (1) to (12), wherein Dt is less than 685 (mm), where Dt (mm) is the outer diameter of the tire when the tire is installed on a standardized rim and the internal pressure is 250 kPa.

The present disclosure (14) is the pneumatic tire of any combination of the present disclosures (1) to (13), wherein the cross-sectional width Wt (mm) is less than 205 mm.

The present disclosure (15) is the pneumatic tire according to the present disclosure (14), wherein the cross-sectional width Wt (mm) is less than 200 mm.

The present disclosure (16) is the pneumatic tire of any combination of the present disclosures (1) to (15), which is a pneumatic tire for a passenger car. 

1. A pneumatic tire having a side portion, wherein the thickness S (mm) of the rubber layer radially outside the carcass of the side portion at the maximum width position of the tire is 3 mm or less; the loss tangent (70° C. tan δ) of the rubber layer is 0.15 or less measured under the conditions of 70° C., frequency of 10 Hz, initial strain of 5%, and dynamic strain rate of 1%; and when the cross-sectional width of the tire is Wt (mm), the outer diameter is Dt (mm), and the volume of the space occupied by the tire is the virtual volume V (mm³), when the tire is installed on a standardized rim and the internal pressure is 250 kPa, the tire satisfies following (formula 1) and (formula 2): 1700≤(Dt ²×π/4)/Wt≤2827.4  (formula 1) [(V+1.5×10⁷)/Wt]≤2.88×10⁵  (formula 2)
 2. The pneumatic tire according to claim 1, wherein the following (formula 3) is satisfied. [(V+2.0×10⁷)/Wt]≤2.88×10⁵  (formula 3)
 3. The pneumatic tire according to claim 2, wherein the following (formula 4) is satisfied. [(V+2.5×10⁷)/Wt]≤2.88×10⁵  (formula 4).
 4. The pneumatic tire according to claim 1, wherein, when the outer diameter of the tire is Dt (mm) and the cross-sectional height of the tire is Ht (mm) when the tire is installed on a standardized rim and the internal pressure is 250 kPa, (Dt−2×Ht) is 470 (mm) or more.
 5. The pneumatic tire according to claim 1, which has an aspect ratio of 40% or more.
 6. The pneumatic tire according to claim 5, which has an aspect ratio of 45% or more.
 7. The pneumatic tire according to claim 6, which has an aspect ratio of 47.5% or more.
 8. The pneumatic tire according to claim 7, which has an aspect ratio of 50% or more.
 9. The pneumatic tire according to claim 1, wherein the following (formula 5) is satisfied: 70° C. tan δ×(V/Wt)×S≤80000  (formula 5).
 10. The pneumatic tire according to claim 9, wherein the following (formula 6) is satisfied: 70° C. tan δ×(V/Wt)×S≤60000  (formula 6).
 11. The pneumatic tire according to claim 10, wherein the following (formula 7) is satisfied: 70° C. tan δ×(V/Wt)×S≤40000  (formula 7).
 12. The pneumatic tire according to claim 11, wherein the following (formula 8) is satisfied: 70° C. tan δ×(V/Wt)×S≤35000  (formula 8).
 13. The pneumatic tire according to claim 1, wherein Dt is less than 685 (mm), where Dt (mm) is the outer diameter of the tire when the tire is installed on a standardized rim and the internal pressure is 250 kPa.
 14. The pneumatic tire according to claim 1, wherein the cross-sectional width Wt (mm) is less than 205 mm.
 15. The pneumatic tire according to claim 14, wherein the cross-sectional width Wt (mm) is less than 200 mm.
 16. The pneumatic tire according to claim 1, which is a pneumatic tire for a passenger car. 